d1 = 15 miles
t1 = 1 hour
d2 = 25 miles
t2 = 2 hours
d = 15 + 25 = 40 miles
t = 1 + 2 = 3 hours
[tex]avg. \: speed \: = \: \frac{total \: distance}{total \: time} [/tex]
[tex]avg. \: speed \: = \frac{40}{3} [/tex]
[tex]avg. \: speed \: = 13.33mi \: hr ^{ - 1} [/tex]
